1. Field of the Invention
The present invention relates to an apparatus and method for probing integrated circuits using external illumination.
2. Description of the Related Art
Probing systems have been used in the art for testing and debugging integrated circuit (IC) designs and layouts. Various laser-based systems for probing IC's are known in the prior art. In these prior art systems, the DUT is driven by an electrical test signal, while a laser beam is used to illuminate the DUT. The laser beam then reflects from the DUT, and the reflection is perturbed according to the DUT's response to the electrical test signals. The reflected beam is then converted to an electrical signal having a waveform corresponding to the reflected beam. This waveform is displayed for the user's analysis.
While some description of the prior art is provided herein, the reader is encouraged to also review U.S. Pat. Nos. 5,208,648, 5,220,403 and 5,940,545, which are incorporated herein by reference in their entirety. Additional related information can be found in Yee, W. M., et al. Laser Voltage Probe (LVP): A Novel Optical Probing Technology for Flip-Chip Packaged Microprocessors, in International Symposium for Testing and Failure Analysis (ISTFA), 2000, p 3-8; Bruce, M. et al. Waveform Acquisition from the Backside of Silicon Using Electro-Optic Probing, in International Symposium for Testing and Failure Analysis (ISTFA), 1999, p 19-25; Kolachina, S. et al. Optical Waveform Probing—Strategies for Non-Flipchip Devices and Other Applications, in International Symposium for Testing and Failure Analysis (ISTFA), 2001, p 51-57; Soref, R. A. and B. R. Bennett, Electrooptical Effects in Silicon. IEEE Journal of Quantum Electronics, 1987. QE-23 (1): p. 123-9; Kasapi, S., et al., Laser Beam Backside Probing of CMOS Integrated Circuits. Microelectronics Reliability, 1999. 39: p. 957; Wilsher, K., et al. Integrated Circuit Waveform Probing Using Optical Phase Shift Detection, in International Symposium for Testing and Failure Analysis (ISTFA), 2000, p 479-85; Heinrich, H. K., Picosecond Noninvasive Optical Detection of Internal Electrical Signals in Flip-Chip-Mounted Silicon Integrated Circuits. IBM Journal of Research and Development, 1990. 34 (2/3): p. 162-72; Heinrich, H. K., D. M. Bloom, and B. R. Hemenway, Noninvasive sheet charge density probe for integrated silicon devices. Applied Physics Letters, 1986. 48 (16): p. 1066-1068; Heinrich, H. K., D. M. Bloom, and B. R. Hemenway, Erratum to Noninvasive sheet charge density probe for integrated silicon devices. Applied Physics Letters, 1986. 48 (26): p. 1811.; Heinrich, H. K., et al., Measurement of real-time digital signals in a silicon bipolar junction transistor using a noninvasive optical probe. IEEE Electron Device Letters, 1986. 22 (12): p. 650-652; Hemenway, B. R., et al., Optical detection of charge modulation in silicon integrated circuits using a multimode laser-diode probe. IEEE Electron Device Letters, 1987. 8 (8): p. 344-346; A. Black, C. Courville, G Schultheis, H. Heinrich, Optical Sampling of GHz Charge Density Modulation in SIlicon Bipolar Junction Transistors Electronics Letters, 1987, Vol. 23, No. 15, p. 783-784, which are incorporated herein by reference in their entirety.
Some of the test and debug technique used in the prior art include LIVA (Light Induced Voltage Alteration), TIVA (Thermally Induced Voltage Alteration), CIVA (Charge Induced Voltage Alteration), XIVA (Externally Induced Voltage Alteration), OBIC (Optical Beam Induced Current), OBHIC (Optical Beam Heat Induced Current), and OBIRCH (Optical Beam Induced Resistance Change). These techniques probe the DUT (device under test) to detect a change in the characteristics of certain devices or structures therein to thereby detect a failure or an area that is prone to fail or adversely affect the DUT's performance. According to these techniques, the DUT is driven by an electrical signal, while a laser beam is used to illuminate the DUT to thereby cause either heating, carrier generation, or both. As a result, the electrical output from the DUT is perturbed, and this perturbation is detected and analyzed. That is, under these techniques the laser beam is used only as a perturbing agent, but the detection is done by analyzing the electrical output from the DUT.
FIG. 1 is a general schematic depicting major components of a laser-based system architecture, 100, according to the prior art. In FIG. 1, dashed arrows represent optical path, while solid arrows represent electronic signal path. The optical paths represented by dashed lines are generally made using fiber optic cables. Probing system 100 comprises a mode-locked laser source MLL 110, an optical bench 112, and data acquisition and analysis apparatus 114. The optical bench 112 includes provisions for mounting the DUT 160 and includes beam optics 125. The beam optics may include various elements to shape the beam, generally shown as beam manipulation optics, BMO 135, and elements for pointing and/or scanning the beam over the DUT, such as a laser scanning microscope, LSM 130. A computer 140 or other device may be used to provide power and/or signals, 142, to the DUT 160, and may provides trigger and clock signals, 144, to the mode-locked laser source 110 and/or the analysis apparatus 114. The analysis apparatus, 114, includes workstation 170, which controls as well as receives, processes, and displays data from the signal acquisition board 150 and the optical bench 112.
In operation, computer 140, which may be a conventional ATE (Automated Testing Equipment, also known as Automated Testing and Evaluation), generates test vectors that are electrically fed to the DUT. The ATE also sends sync signal to the mode-locked laser source, which emits a laser beam. The beam optics 125 is then used to point the beam to illuminates various positions on the DUT. The beam reflects from the DUT, but the reflection is perturbed by the DUT's response to the test vectors. This perturbed reflection is detected by photodetector 136, which converts it into an analog signal. The analog signal is acquired by the signal acquisition board 150 and is fed to computer 170, where it is displayed as a waveform corresponding to the perturbed reflection from the DUT. By correlating the timeline of the waveform to that of the ATE, the response of the DUT can be analyzed.
While the arrangement depicted in FIG. 1 has been used successfully in the art, there is a constant search for new systems that can provide further information regarding the operation and characteristics of the DUT. Accordingly, there is a need in the art for a system that will allow improved laser probing of a DUT to enable further investigation of chip designs.